1. Field of the Invention
The present invention relates generally to a position determining device, and more particularly to a position determining device that is used suitably for a position determining device for determining the operated amount of a control member in a control unit that controls the focus, zoom, etc. of a TV camera lens electrically, and a position determining device for determining the position of a lens in the TV camera lens.
2. Description of Related Art
Generally, a control unit that controls the zoom and focus of a TV camera lens uses a potentiometer and a rotary encoder to determine the operated amount of a control member such as a control ring and a control knob. For instance, a control knob that rotates once to three times is widely used in a focus control unit for the TV camera lens. In such a control unit, the control knob has rotational limits, and therefore, an absolute position determiner such as a potentiometer and an absolute rotary encoder is preferably used for a determiner that determines the operated amount of the control knob.
The absolute rotary encoder, however, is not advantageous in view of the price, size, distinguishability and consumption of electricity, and is not a desirable means at present.
On the other hand, the incremental rotary encoder works more reliably and has higher linearity between output signals and the operated amount than the potentiometer. If the incremental rotary encoder is used, however, a cameraman must move the control part to a reference position (e.g., one of the rotational limits) to initialize the control unit upon turning on the control unit. This is not desirable in view of the convenience. Moreover, even in the case that the present position of the control part is recorded in a memory, etc. before the control unit is turned off, the position recorded in the memory does not correspond to the actual position if the control part is operated and moved while the control unit is off.